In vitro and in vivo evaluations of a hydrophilic 64Cu-bis(thiosemicarbazonato)-glucose conjugate for hypoxia imaging.
A water-soluble glucose conjugate of the hypoxia tracer 64Cu-diacetyl-bis(N4-methylthiosemicarbazone) (64Cu-ATSM) was synthesized and radiolabeled (64Cu-ATSE/A-G). Here we report our initial biological experiments with 64Cu-ATSE/A-G and compare the results with those obtained for 64Cu-ATSM and 18F-FDG.


METHODS
The uptake of 64Cu-ATSE/A-G and 64Cu-ATSM into HeLa cells in vitro was investigated at a range of dissolved oxygen concentrations representing normoxia, hypoxia, and anoxia. Small-animal PET with 64Cu-ATSE/A-G was performed in male BDIX rats implanted with P22 syngeneic carcinosarcomas. Images of 64Cu-ATSM and 18F-FDG were obtained in the same model for comparison.


RESULTS
64CuATSE/A-G showed oxygen concentration-dependent uptake in vitro and, under anoxic conditions, showed slightly lower levels of cellular uptake than 64Cu-ATSM; uptake levels under hypoxic conditions were also lower. Whereas the normoxic uptake of 64Cu-ATSM increased linearly over time, 64Cu-ATSE/A-G uptake remained at low levels over the entire time course. In the PET study, 64CuATSE/A-G showed good tumor uptake and a biodistribution pattern substantially different from that of each of the controls. In marked contrast to the findings for 64Cu-ATSM, renal clearance and accumulation in the bladder were observed. 64Cu-ATSE/A-G did not display the characteristic brain and heart uptake of 18F-FDG.


CONCLUSIONS
The in vitro cell uptake studies demonstrated that 64Cu-ATSE/A-G retained hypoxia selectivity and had improved characteristics when compared with 64Cu-ATSM. The in vivo PET results indicated a difference in the excretion pathways, with a shift from primarily hepatointestinal for 64Cu-ATSM to partially renal with 64Cu-ATSE/A-G. This finding is consistent with the hydrophilic nature of the glucose conjugate. A comparison with 18F-FDG PET results revealed that 64Cu-ATSE/A-G was not a surrogate for glucose metabolism. We have demonstrated that our method for the modification of Cu-bis(thiosemicarbazonato) complexes allows their biodistribution to be modified without negating their hypoxia selectivity or tumor uptake properties.
Bayly
Simon R
SR
Siemens Oxford Molecular Imaging Laboratory, Inorganic Chemistry Laboratory, University of Oxford, Oxford, United Kingdom.
King
Robert C
RC
Honess
Davina J
DJ
Barnard
Peter J
PJ
Betts
Helen M
HM
Holland
Jason P
JP
Hueting
Rebekka
R
Bonnitcha
Paul D
PD
Dilworth
Jonathan R
JR
Aigbirhio
Franklin I
FI
Christlieb
Martin
M
D000818:Animals; D002296:Carcinosarcoma / Q000000981:diagnostic imaging; D003301:Copper Radioisotopes / Q000737:chemistry*; D019788:Fluorodeoxyglucose F18; D005947:Glucose / Q000737:chemistry*; D006367:HeLa Cells; D006801:Humans; D000860:Hypoxia / Q000000981:diagnostic imaging* / Q000378:metabolism; D008297:Male; D010100:Oxygen / Q000378:metabolism; D049268:Positron-Emission Tomography; D051381:Rats; D013882:Thiosemicarbazones / Q000097:blood / Q000737:chemistry* / Q000378:metabolism*
D003301:Copper Radioisotopes; D013882:Thiosemicarbazones; D019788:Fluorodeoxyglucose F18; D005947:Glucose; D010100:Oxygen